The primary objectives of this study are to yield descriptions of prescribing practices of nurse practitioners and to ferret out conditions that may be associated with variability of those practices. As state licensure boards have adopted varying types of restrictions on prescriptive authority of nurses, thus have placed varying limits on nurse autonomy in prescribing decisions and actions, particular attention is given to the effect of these legal constraints on prescribing practices of nurses. The projected sample, estimated as 400, is practitioners in four Northwest states who hold prescribing privileges. Data production will use mail survey research techniques employing three instruments (two questionnaires and a prescription log) developed for this study. Data will include characteristics of prescriptions issued over a 10-day period (estimated as 12,000), of clients receiving prescriptions, and of nurse practitioners and their work settings. Analyses will be descriptive and exploratory. Selected data will be compared with reported prescribing practices of physicians. Study findings will be examined for their policy implications for prescribing privileges of nurse practitioners and as they relate to availability and accessibility of primary care for underserved populations. Implications for future cost effectiveness research and for nurse practitioner preparation also will be considered.